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ftell.c revision 1.3 
      1 /*-
      2  * Copyright (c) 1990 The Regents of the University of California.
      3  * All rights reserved.
      4  *
      5  * This code is derived from software contributed to Berkeley by
      6  * Chris Torek.
      7  *
      8  * Redistribution and use in source and binary forms, with or without
      9  * modification, are permitted provided that the following conditions
     10  * are met:
     11  * 1. Redistributions of source code must retain the above copyright
     12  *    notice, this list of conditions and the following disclaimer.
     13  * 2. Redistributions in binary form must reproduce the above copyright
     14  *    notice, this list of conditions and the following disclaimer in the
     15  *    documentation and/or other materials provided with the distribution.
     16  * 3. All advertising materials mentioning features or use of this software
     17  *    must display the following acknowledgement:
     18  *	This product includes software developed by the University of
     19  *	California, Berkeley and its contributors.
     20  * 4. Neither the name of the University nor the names of its contributors
     21  *    may be used to endorse or promote products derived from this software
     22  *    without specific prior written permission.
     23  *
     24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     34  * SUCH DAMAGE.
     35  */
     36 
     37 #if defined(LIBC_SCCS) && !defined(lint)
     38 /*static char *sccsid = "from: @(#)ftell.c	5.4 (Berkeley) 2/5/91";*/
     39 static char *rcsid = "$Id: ftell.c,v 1.3 1993/08/26 00:46:58 jtc Exp $";
     40 #endif /* LIBC_SCCS and not lint */
     41 
     42 #include <stdio.h>
     43 #include <errno.h>
     44 #include "local.h"
     45 
     46 /*
     47  * ftell: return current offset.
     48  */
     49 long
     50 ftell(fp)
     51 	register const FILE *fp;
     52 {
     53 	register fpos_t pos;
     54 
     55 	if (fp->_seek == NULL) {
     56 		errno = ESPIPE;			/* historic practice */
     57 		return (-1L);
     58 	}
     59 
     60 	/*
     61 	 * Find offset of underlying I/O object, then
     62 	 * adjust for buffered bytes.
     63 	 */
     64 	if (fp->_flags & __SOFF)
     65 		pos = fp->_offset;
     66 	else {
     67 		pos = (*fp->_seek)(fp->_cookie, (fpos_t)0, SEEK_CUR);
     68 		if (pos == -1L)
     69 			return (pos);
     70 	}
     71 	if (fp->_flags & __SRD) {
     72 		/*
     73 		 * Reading.  Any unread characters (including
     74 		 * those from ungetc) cause the position to be
     75 		 * smaller than that in the underlying object.
     76 		 */
     77 		pos -= fp->_r;
     78 		if (HASUB(fp))
     79 			pos -= fp->_ur;
     80 	} else if (fp->_flags & __SWR && fp->_p != NULL) {
     81 		/*
     82 		 * Writing.  Any buffered characters cause the
     83 		 * position to be greater than that in the
     84 		 * underlying object.
     85 		 */
     86 		pos += fp->_p - fp->_bf._base;
     87 	}
     88 	return (pos);
     89 }
     90